1. Field
Embodiments described herein generally relate to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
As one of power semiconductor devices, a so-called DMOS transistor is known. The DMOS transistor has a drift region which is adjacent to a drain diffusion layer having a high impurity concentration, and which is of the same conductive type as this drain diffusion layer and has a lower impurity concentration than the drain diffusion layer. The DMOS transistor has characteristics that a switching speed is high and conversion efficiency is high in a comparatively low voltage area, and can achieve both of a high breakdown voltage operation and low on-resistance.
The high breakdown voltage of the DMOS transistor is realized by optimally designing a depletion layer, and the low on-resistance is realized by optimizing a cell resistance of a unit element. However, the high breakdown voltage and low on-resistance have a trade-off relationship, and an optimal structure for the high breakdown voltage and an element structure for obtaining the low on-resistance need to be optimized. While resistance components of the DMOS transistor include, for example, a diffusion layer resistance, channel resistance, drift layer resistance and wiring resistance, the wiring resistance is a resistance component which is little influenced by an element design on the semiconductor substrate. It is necessary to reduce the wiring resistance to have the low on-resistance without decreasing the breakdown voltage.